Funny, I seem to not listen to any artists who are around for long enough to have a downhill turnaround album. I suppose that's what you get when you listen to Seattle groups artists. My favorite band of all time, Screaming Trees, released 7 albums in ten years, but they only steadily got better (and Allmusic seems to agree with me).

The only close example I can think of is Pearl Jam. But they rebounded after their descent. Basically, they lost me at "No Code", but got me back at "Binaural."